1. Field of the Invention
The present invention relates to a transfer method for devices or circuits, and a circuit board, an electro-optical apparatus, an IC card and an electronic appliance manufactured using the transfer method.
2. Description of the Related Art
Recently, with regard to the manufacture of electro-optical apparatuses such as liquid crystal electro-optical apparatuses having thin film devices such as thin film transistors (TFTs) or thin film diodes (TFDs), there has been research into various art for reducing the amount of thin film device-constituting material discarded through etching and thus greatly reducing the manufacturing cost of the electro-optical apparatuses.
Conventionally, a method developed by Alien Technology called the microstructure technique is known as art for disposing, on a separate substrate, LSI circuits that have been manufactured on a silicon wafer (Information Display, Vol. 15, No. 11 (November 1999)). This microstructure technique is characterized in that the LSI circuits that have been manufactured on the silicon wafer are separated to form microchips (i.e. microstructures), and then a solvent in which the microstructures have been dispersed is made to flow over a substrate in which a pattern of holes for embedding has been formed in advance, thus disposing the microstructures in specific positions on the substrate. According to this microstructure technique, a large number of microstructures that have been formed in advance on a silicon wafer can be disposed in scattered locations on a substrate.
However, with this microstructure technique, there is a drawback in that disposing the microstructures on the substrate with certainty and carrying out accurate alignment are difficult. Furthermore, the directions in which the microstructures are disposed are random, and hence it has been necessary to provide special circuits on the microstructures, for example circuits having symmetry.
Moreover, in the case of the manufacture of color filters for liquid crystal displays, a method in which a transfer technique is used is disclosed in U.S. Pat. No. 6,057,067.
Furthermore, the present applicants have developed, as a method of transferring, onto a transfer body, thin film devices such as TFTs that have been formed on a substrate, a transfer method in which a transferred layer is formed on the substrate via a peeling layer, this is all joined to the transfer body, and then the peeling layer is irradiated with light to bring about peeling, and the substrate is separated away from the peeling layer, and have already filed a patent application (Japanese Patent Application Laid-open No. 10-125931). Similarly, the present applicants have developed a transfer method in which the whole of a transferred layer is joined to a primary transfer body, and then transfer is further carried out onto a secondary transfer body, and have already filed a patent application (Japanese Patent Application Laid-open No. 11-26733).
According to these transfer techniques, functional devices that require a high-temperature process during manufacture can be transferred onto desired substrates, including ones that cannot withstand such high temperatures.
However, with the conventional transfer techniques described above, there have been problems such as the following.
With the above transfer techniques, if an apparatus substrate is formed by transferring onto a transfer destination substrate the whole of a thin film device layer that has been formed on a transfer origin substrate, then, as with conventionally, a process in which the transfer destination substrate is divided into pieces of the required chip size (or small substrate size) by dicing or the like is still necessary. Moreover, in the process of assembling on the final substrate, it is necessary to accurately arrange on the final substrate chips or the like that have become scattered about. This is surprisingly troublesome, and hence there has been a problem that the manufacturing efficiency is prone to dropping.
Moreover, with the above transfer techniques, all of the thin film devices such as TFTs formed on the transfer origin substrate are transferred onto the transfer destination substrate, and hence the larger the area of the substrate, the better the properties, i.e. the higher the output power, the uniformity and so on, required of the laser light irradiated, and hence it becomes difficult to obtain a laser light source that meets the required performance, and moreover large, high-accuracy irradiation equipment becomes necessary for the laser light irradiation. Furthermore, if laser light of high output power is irradiated, then there is a risk that the thin film devices may be heated to a temperature above the limit of heat resistance thereof, resulting in the functions of the thin film devices themselves being lost, and hence there has been a problem that the transfer process itself becomes difficult.
Consequently, it is an object of the present invention to provide a transfer method according to which some only of a plurality of devices or circuits can be transferred between substrates during thin film apparatus manufacture, without it being necessary to carry out a step of dividing (dicing) into chips or the like.
Moreover, it is an object of the present invention to provide a transfer method according to which some of a plurality of devices or circuits formed on a substrate can be transferred directly from the substrate to another transferred body such as a circuit board.